The present invention relates to motors of the fractional revolution type or torque motors as they are commonly called. Motors of this type typically provide angular displacement or movement of the rotor based on an applied electrical signal as, for example, angular rotor movement proportional to the applied voltage or level of current flow through the motor winding. However, the invention may have broader applications wherever a particular vibration is advantageously used to assure a desired movement.
Torque motors have found widespread application in control systems where it is desired to rotate a shaft or member to a specific position or to apply a specified amount of torque to a shaft in response to an electrical control signal. In particular, in the auto industry, torque motors have been utilized to control the position of an internal combustion engine air inlet throttle valve by an electrical signal instead of directly by user movement of a mechanical throttle linkage attached to the throttle valve. The desirability of electrical engine throttle valve control has arisen in certain motor vehicle applications where it is desired to provide cruise control and/or override the user input to the throttle position control mechanism in response to the vehicle encountering extreme driving conditions or emergency situations. For example, where an anti-lock brake or traction control system is employed on the vehicle, it is desired under certain conditions to have the electronic control system intervene to determine the throttle valve position rather than the user inputs to the accelerator pedal control. Accordingly, it is expected that demand for electrical valve control will continue to increase and use of mechanical linkages will wane.
Under certain motor vehicle operating conditions, it is possible for ice to form on and around the throttle plate valve of a motor vehicle electronic throttle control. In such situations, movement of the throttle plate in response to torque applied by the torque motor is prevented. Of course, safe and effective vehicle operation is not possible under such conditions. With prior, purely mechanical throttle plate position control linkages, an operator of the vehicle was able to overcome the ice simply by application of increased force on the accelerator pedal. In addition to ice, with the close manufacturing tolerances used in vehicle electronic throttle assemblies, it is possible that dirt or other debris may jam the throttle plate and prevent movement under the control of the subject torque motor.
Heretofore, the solution to these problems has been to use a torque motor having a sufficiently high torque output that ice and other obstructions can be overcome by the motor without difficulty. Unfortunately, use of large, high-output torque motors is not efficient in terms of motor cost and space requirements. For example, the required operational torque for electronic throttle operation under "normal" conditions (with no icing or other obstruction) is approximately 25% of the torque output by these prior motors, i.e., prior motors have been selected for electronic throttle control based upon "ice breaking" rather than typical operational requirements.
In light of the foregoing, it is now desirable to develop a torque motor system and method of operation for use in an electronic throttle control system or other mechanical system that allows a torque motor to be selected based upon the normal operating torque output required from the motor and not ice breaking or other obstruction clearing requirements. Use of such motors rather than larger, higher-output motors would reduce manufacturing cost, motor space requirements, and facilitate use as a high-volume motor vehicle component and other usage.